(a) Field of the Invention
This invention relates to a compact zoom lens system for use in a lens-shutter camera.
(b) Description of the prior art
Recently, together with the progress in compactness of cameras, there has also been an attempt to make a zoom lens system compact and light. Especially, in a lens-shutter camera in which objective lens systems cannot be exchanged, there has been required a camera having a compact zoom lens system with a zooming ratio of about 2.
As a zoom lens system which satisfies the above-mentioned requirements, there has been known a zoom lens system comprising a front lens group having a positive refracting power and a rear lens group having a negative refracting power and being arranged to be zoomed by varying the space between these lens groups, which lens system has been disclosed, for example, in Japanese Published Unexamined Patent Application No. 159612/86. In order to make the lens system having such lens configuration more compact, the radius of curvature of each lens-surface may be made smaller so that the power of each lens may become stronger. In this case, however, the fluctuation of aberrations during a zooming operation becomes large, which makes it impossible to correct aberrations favorably and to make the zooming ratio large. In order to decrease the fluctuation of aberrations during a zooming operation, to correct aberrations favorably and to obtain a sufficient zooming ratio, the number of lens components needs to be increased so that the lens system becomes large as a whole, which is contrary to the requirement of compactness. When the power of each lens is made weaker in order to decrease the fluctuation of aberrations during a zooming operation, the moving amount of each lens group will become larger so that it becomes impossible to make the lens system compact.
It has been known that, in order to overcome the above-mentioned problems, a zoom lens system employed a graded refractive index lens, as disclosed in Japanese Published Unexamined Patent Application Nos. 148414/86, 259216/86, 295524/86. In such a zoom lens system, however, the number of lens components thereof is no less than 5 so that these lens systems cannot be said to be compact and sufficiently light.